Ion implanted substrate having capping layer and method

ABSTRACT

In an ion implantation method, a substrate is placed in a process zone and ions are implanted into a region of the substrate to form an ion implanted region. A porous capping layer comprising dispersed gas pockets is deposited on the ion implanted region.

CROSS-REFERENCE

The present application is a continuation of U.S. patent applicationSer. 12/367,306, filed on Feb. 6, 2009, entitled “Ion ImplantedSubstrate Having Capping Layer and Method”, which is being incorporatedherein by reference in its entirety.

BACKGROUND

Embodiments of the present invention relate to implanting ions in asubstrate to form ion implantation regions.

Ion implanted regions are formed on a substrate to change the energyband gap level of material in a region of the substrate. For example,ions of boron, phosphorous arsenic, and other materials, are implantedin silicon or compound semiconductor materials to form semiconductingregions. As another example, ions are implanted in substrates comprisingquartz, group III or group V compounds (e.g. GaAs), to form photovoltaiccells for solar panels. As yet another example, ions are implanted insubstrates comprising gallium nitride to form light emitting diode (LED)for display panels.

However, in some ion implantation processes, a large percentage of theimplanted ions evaporate or volatilize during the ion implantationprocess, or afterwards in subsequent processes. For example, diffusionand volatilization of implanted ions can occur in annealing processeswhich are performed after an ion implantation process is completed. Asan example, ion implanted regions of a substrate comprising a siliconwafer are annealed to more uniformly distribute the ions in the implantregions, electrically activate the implant, and remove lattice defects.Such an annealing process can be conducted by heating the substrate to atemperature of at least about 950° C. However, the heat applied duringthe annealing process can cause the implanted ions to volatilize fromthe substrate, especially for high ion concentrations in shallowjunctions.

For reasons including these and other deficiencies, and despite thedevelopment of various ion implantation methods and structures, furtherimprovements in ion implantation technology are continuously beingsought.

SUMMARY

In an ion implantation method, a substrate is placed in a process zoneand ions are implanted into a region of the substrate to form an ionimplanted region. A porous capping layer comprising dispersed gaspockets is deposited on the ion implanted region.

In another ion implantation method, a substrate is placed in a processzone and ions are implanted into a region of the substrate to form anion implanted region. A porous capping layer comprising dispersedmicroscopic gas pockets is deposited on the ion implanted region. Thesubstrate is annealed to volatize at least 80% of the porous cappinglayer overlying the ion implanted region during the annealing process.

In yet another ion implantation method, arsenic ions are implanted intoa region of a substrate to form an ion implanted region. A porouscapping layer comprising silicon-containing material having dispersedmicroscopic gas pockets is deposited on the ion implanted region. Thesubstrate is annealed to volatize at least 80% of the porous cappinglayer overlying the ion implanted region during the annealing process.

DRAWINGS

These features, aspects and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings, which illustrate examples ofthe invention. However, it is to be understood that each of the featurescan be used in the invention in general, not merely in the context ofthe particular drawings, and the invention includes any combination ofthese features, where:

FIGS. 1A and 1B are cross-sectional schematic side views of an ionimplantation process being performed on a substrate to form a pluralityof ion implanted regions in the substrate;

FIG. 1C is a cross-sectional schematic side view of the substrate ofFIG. 1B, showing a porous capping layer being deposited over the ionimplanted regions to form an intermediate product;

FIG. 1D is a cross-sectional schematic side view of the substrate ofFIG. 1C showing annealing of the ion implanted regions and the cappinglayer being vaporized in the annealing process;

FIG. 1E is a cross-sectional schematic side view of the substrate ofFIG. 1D after the capping layer has been vaporized from the ionimplanted regions;

FIG. 2 is a flowchart of the ion implantation, capping, and vaporizationprocesses;

FIG. 3 is a cross-sectional schematic view of an integrated circuitcomprising PMOS and NMOS transistors; and

FIG. 4 is a cross-sectional schematic side view of an apparatus suitablefor practicing the ion implantation and capping processes.

DESCRIPTION

In a process for fabricating a substrate 40 for semiconductor, solarpanel, LED and other applications, a plurality of ion implanted regions44 a,b are formed on the substrate as shown in FIGS. 1A and 1B. Thesubstrate 40 may be a material such as, for example, any one or more ofsilicon oxide, silicon carbide, crystalline silicon, strained silicon,silicon germanium, doped or undoped polysilicon, doped or undopedsilicon wafers, doped silicon, germanium, gallium arsenide, galliumnitride, glass, sapphire and quartz. The substrate 40 can have differentdimensions, for example, the substrate 40 can be a circular wafer havinga diameter of 200 mm or 300 mm, or a rectangular or square panel.

The ions 45 implanted in the ion implantation regions 44 a,b depend uponthe application of the substrate 40. For example, the ion implantationregions 44 a,b can be used to form gate and/or source drain structuresof a transistor of an integrated circuit chip by implanting n-type andp-type dopants into a substrate 40 comprising a silicon wafer. Suitableions 45 that form n-type dopants when implanted in silicon include, forexample, at least one of phosphorous, arsenic, antimony and combinationsthereof. Suitable ions 45 that form p-type dopants include, for example,at least one of boron, aluminum, gallium, thallium, indium, silicon andcombinations thereof. Thus, when a p-type conductivity dopant such asboron is implanted into silicon in an ion implantation region 44 a,b,which is adjacent to another ion implantation region (not shown) whichhas been previously doped with an n-type dopant such as arsenic orphosphorous, then a p-n junction is formed along the boundary betweenthe two regions. The ions can be implanted to a selected dosage levelof, for example, a dosage of from 1×10¹⁴ atoms/cm³ to 1×10¹⁷ atoms/cm³.

In the implantation process, the substrate 40 is placed in a processzone 46 and the substrate temperature is maintained at between about 25°C. and about 400° C. A process gas is introduced into the process zone46 to provide the ion source species to be implanted. The process gascan also include a volatile species such as fluorine and/or hydrogen.For example, the process gas can include ion implantation gasescomprising the fluorides and/or hydrides of arsenic, boron, phosphorous,etc. The ion implantation gas can include, for example, AsF₃, AsH₃,B₂H₆, BF₃, SiH₄, SiF₄, PH₃, AsF₅, P₂H₅, P0 ₃, PF₃, PF₅ and CF₄. Thefluoride and the hydride of a particular gas can also be combined, forexample, BF₃+B₂H₆, PH₃+PF₃, AsF₃+AsH₃, SiF₄+SiH₄, or GeF₄+GeH₄. In oneembodiment, the ion implantation gas can have a flow rate of betweenabout 2 sccm and about 1000 sccm.

The process gas can further include an inert or nonreactive gas, such asN₂, Ar, He, Xe, and Kr. The inert or nonreactive gas promotes the ionbombardment to increase process gas collisions and reduce recombinationof ion species. The flow rate of the inert or non-reactive gas can befrom about 10 sccm to about 1200 sccm.

The process gas can further include a nitrogen-containing gas to assistthe formation of the volatile byproducts which are more readily pumpedout of the processing chamber. The nitrogen containing gas may includeNO, NO₂, NH₃, N₂, N₂O and mixtures thereof. The nitrogen-containing gascan be supplied at a flow rate of from about 10 sccm to about 500 sccm.

The process gas is ionized to form a plasma 48 containing ions 45 of theatomic species to be implanted to the substrate 40. These ions areaccelerated (as shown by the arrows 50 in FIGS. 1A and 1B) by a voltagepotential applied across to process zone 46 to form ions thatenergetically impinge upon, and enter into, the exposed regions 52 ofthe substrate 40 to form ion implanted regions. The process gas can beenergized by source power which is inductively coupled power applied toantennas (not shown) about the process zone 46, and a bias power whichis capacitively coupled power applied to electrodes (not shown) aboutthe process zone 46, or combinations of source and bias power.Typically, the source power generates the plasma 48 from the processgas, and the bias power further dissociates the process gas and alsoaccelerates the dissociated ions 45 toward the substrate 40. The sourceand bias power are set to predefined energy levels to allow the ionspecies to be driven to the desired depth into the substrate 40.Dissociated ions with low ion energy are implanted at a shallow depth ofless than 500 Å, for example, from about 10 Å to about 500 Å from thesubstrate surface. Dissociated ions with high ion energy generated fromhigh RF power, for example higher than about 10 KeV, may be implantedinto the substrate 40 to a depth of over 500 Å from the substratesurface. In one example, the source power is maintained at from about 50to about 2000 Watts, and the bias power is maintained at from about 50to about 11000 Watts with an RF voltage of from about 10 to about 12000Volts.

In an exemplary embodiment, arsenic ions can be implanted into asubstrate 40 in a process zone 46. The substrate 40 is maintained at atemperature of less than 30° C. In this process, a process gascomprising an arsenic-containing gas, such as AsH₃, is introduced intothe process zone 46. The process gas is maintained at a pressure of fromabout 3 mTorr to about 2 Torr, for example about 20 mTorr. The processgas is energized to form a plasma by powering an antenna (not shown)about the process zone 46, at a voltage of from about 200 to about 8000volts, for example, about 6000 volts. The source power applied to theantenna can be from about 100 to about 3000 Watts, for example, about1000 Watts. The resultant plasma comprises energized arsenic ions thatare implanted into the substrate 40 to form ion implanted regions 44 a,bcomprising arsenic-implanted regions. The arsenic ions are implanted toa depth of less than 500 Å from the substrate surface in a dosage of atleast about 1×10¹⁶ atoms/cm³.

In a prospective example, boron ions can be implanted into the substrate40 from a plasma of a process gas comprising a boron-containing gas suchas, for example, boron trifluoride gas (BF₃). The process gas isenergized to generate a plasma of sufficient energy density todissociate the BF₃ molecules, thereby forming ions of B⁺, as well asBF⁺, and possibly BF₂ ⁺. The process gas is maintained at a pressure offrom about 5 mTorr to about 3 Torr. Decaborane powder, which has a vaporpressure of the order of 0.1 Torr at room temperature, and produces asubstantial vapor pressure at temperatures above 100° C., can also beused as a source, or to supplement a gaseous source, of boron ions.

In another prospective example, which represents an exemplary boronimplantation process, the process gas includes BF₃ and SiH₄, which aredissociated as ion species by the plasma in the form of B³⁺, BF²⁺, BF₂²⁺, F , Si₄ and H. The active hydrogen species provided by SiH₄ gasreacts with dissociated F species and other dissociated byproducts, toform HF or other types of volatile species, thus preventing the Fspecies and other types of the byproducts being implanted into thesubstrate 40. Thus, the SiH₄ gas flow is selected to prevent the excessor dissociated Si ions from forming an undesired silicon film on thesubstrate. In one embodiment, the process gas comprises BF₃ and SiH₄ ina flow ratio of from about 1:50 to about 1:100. For example, the BF₃flow rate can be from about 50 to about 400 sccm, and the SiH₄ flow ratecan be from about 1 to about 20 sccm. The source RF power is set fromabout 100 Watts to about 2000 Watts and the bias RF power is set fromabout 100 Volts to about 12000 Volts. The resultant plasma implantsboron ions into the substrate 40 to form ion implanted regions 44 a,bcomprising boron-implanted regions.

In a further prospective example, phosphorous doping can be performedusing a process gas comprising a phosphorous-containing gas such as, forexample, a phosphorous fluoride gas such as, for example, PF₃ or PF₅, ora phosphorous hydride gas such as PH₃. The process gas is introducedinto the process zone 46 and maintained at a pressure of from about 10mTorr to about 3 Torr. For example, PF₃ gas can be supplied at a flowrate of from about 50 sccm to about 1000 sccm. The source RF power maybe set from about 100 watts to about 3000 Watts and the bias RF powermay be set from about 100 Volts to about 12000 Volts. The resultantplasma implants phosphorous ions into the substrate 40 to form the ionimplanted regions 44 a,b comprising phosphorus-implanted regions.

In an exemplary embodiment, after implantation of the ions, a porouscapping layer 54 is deposited on the ion implanted regions 44 a,b asshown in the flow chart of FIG. 2. The porous capping layer 54 coversthe ion implanted regions 44 a,b to form an intermediate product 55, asshown in FIG. 10. The porous capping layer 54 is provided to prevent thevolatilization of ions implanted in the ion implantation regions 44 a,bin subsequent processes such as, for example, an annealing process.However, the annealing process can cause a large portion of theimplanted ions to evaporate or volatilize off the substrate 40,especially when the implanted ions have a low mass, low binding energy,or low solubility with the substrate. The porous capping layer 54 wasdiscovered to reduce the volatilization losses of the implanted ions,thereby preserving a larger percentage of ions within the implantedregions 44 a,b, even after the annealing process.

It was further discovered that the porous capping layer 54 can be easilyvaporized and removed after, or during, the annealing process. It isalso believed that the porosity of the porous capping layer 54 allowsvaporized material emanating from underlayer(s) to more easily escapeand pass through the pores of the capping layer 54. This prevents theporous capping layer 54, when strongly bonded or adhered tounderlayer(s), from delaminating with an attached underlayer. Also, theporous capping layer 54 has less mass because much of the volume istaken up by empty pore space, and accordingly, the layer 54 requiresless energy to be vaporized off the substrate 40. Thus, in one version,the porous capping layer 54 comprises a porosity of at least 20%, oreven at least 50%. Further, the porous capping layer 54 can havecontinuous pores with a pore volume of at least 20%, or even at leastabout 50%. The continuous pores are desirable as they more easily allowvaporization gases and byproducts to escape through the porous cappinglayer 54 without delamination.

In one version, the porous capping layer 54 comprises silicon- andoxygen-containing material. In this version, the porous capping layer 54is deposited by introducing a process gas comprising silicon- andoxygen-containing gas into the process zone 46 and energizing theprocess gas to form a plasma using a plasma enhanced (PECVD) ormicrowave enhanced chemical vapor deposition (MECVD) process to depositsilicon dioxide. While silicon dioxide is described to illustrate thepresent process, it should be noted that other materials can also beused to form the porous capping layer 54. Also, the deposited siliconand oxygen material can include carbon, hydrogen or even nitrogen. Forexample, the porous capping layer 54 of silicon dioxide can be depositedwith a process gas comprising a silicon-containing gases, such as forexample, silane (SiH₄), disilane, dichlorosilane, trichlorosilane, andtetraethylorthosilane, methylsilane (CH₃SiH₃), dimethylsilane((CH₃)₂SiH₂), trimethylsilane ((CH₃)₃SiH), diethylsilane ((C₂H₅)₂SiH₂),propylsilane (C₃H₈SiH₃), vinyl methylsila (CH₂═CH)CH₃SiH₂),1,1,2,2-tetramethyl disilane (HSi(CH₃)₂-Si(CH₃)₂H), hexamethyl disilane((CH₃)₃Si—Si(CH₃)₃), 1,1,2,2,3,3-hexamethyl trisilane(H(CH₃)₂Si—Si(CH₃)₂-SiH(CH₃)₂), 1,1,2,3,3-pentamethyl trisilane(H(CH₃)₂Si—SiH(CH₃)—SiH(CH₃)₂), and other silane related compounds. Theprocess gas can also include an oxygen-containing gas, such as oxygen(O₂), nitrous oxide (N₂O), ozone (O₃), and carbon dioxide (CO₂).

The intermediate product 55 comprising the deposited porous cappinglayer 54 comprising silicon/oxygen containing material has microscopicgas pockets that are uniformly dispersed in a silicon oxide layer. Inone exemplary version, a capping layer 54 comprising porous siliconoxide is deposited on the substrate 40 in the same process zone 46. Aprocess gas comprising a silicon-containing gas and an oxygen-containinggas is introduced into the process zone 46. For example, the process gascan include silane and oxygen, in a volumetric flow ratio of from about1:1 to about 1:10, or even from about 1:2 to about 1:6. For example, theflow rate of silane can be from about 5 to about 50 sccm, and the flowrate of oxygen can be from about 20 to about 200 sccm. Optionally, argonis added to the process gas. When argon is added, the volumetric flowratio of silane to oxygen is maintained at the levels described above,and sufficient argon is added to maintain the oxygen to argon volumetricflow ratio at from about 1:4 to about 4:1. The process gas is maintainedat a pressure of from about 5 mTorr to about 500 mTorr, for exampleabout 100 mTorr. The plasma is generated from RF energy applied to anantenna about the process zone 46 at a voltage of from about 200 toabout 10,000 volts, for example about 1000 volts, and at power level offrom about 1000 watts to about 10,000 watts, for example, about 8000Watts. The substrate 40 is maintained at a temperature of less than 30°C. to cause a porous capping layer 54 to form on the substrate.

In another prospective example, the porous capping layer 54 is formedwith a process gas comprising a silicon-containing gas comprisingtrimethylsilane ((CH₃)₃-SiH) and oxygen. The trimethlysilane is providedat a flow rate of from about 20 to about 100 sccm and oxygen at a flowrate of from about 10 to about 200 sccm. The process gas can alsoinclude helium or nitrogen at a flow rate of from about 10 to about 5000sccm. The chamber pressure is maintained at between about 1 and about 15Torr. An RF power source is applied at from about 100 to about 900watts. The substrate 40 is maintained at a temperature of from about300° to about 450° C., to deposit the porous capping layer 54.

As yet another prospective example, the porous capping layer 54 isdeposited using a process gas comprising tetraethylorthosilane (TEOS) ata flow rate of from about 200 from about 2000 sccm, and oxygen at a flowrate of from about 200 to about 2000 sccm. The plasma is powered with RFenergy at from about 300 to about 1200 Watts. The substrate 40 ismaintained to temperature from about 300 to about 500° C.

The ion implanted regions 44 a,b having the overlying the porous cappinglayer 54 are annealed to more uniformly distribute the ions implantedinto the ion implanted regions, as shown in FIGS. 1D and 2. For example,an ion concentration variation of 1×10¹⁷ atm/cm² can be reduced to1×10¹³ atm/cm² in an annealing process. The annealing process can alsoremove, or reduce, the lattice defects in the ion implanted regions 44a,b which can be caused by the energetic impingement of the implantedions. The annealing process can also be used to activate the implantedions. In one exemplary annealing process, the substrate 40 is heated toa temperature of at least about 1000° C., or even from about 800° C. toabout 1300° C. A suitable annealing process can be performed for about 5minutes.

In the annealing process, at least a portion of the porous capping layer54 volatizes during the heat treatment process. In one version, at least80% of the porous capping layer 54 overlying the ion implanted region isvolatilized during annealing. For example, during annealing, at least90% of the porous capping layer 54 can be volatilized while stillretaining at least 60% of the implanted ions within the ion implantationregions 44 a,b. Thus the porous capping layer 54 retains ions within theion implantation regions 44 a,b, while simultaneously vaporizing off thesubstrate 40. Advantageously, this process allows retention of a largepercentage of the implanted ions while removing substantially all of theporous capping layer 54.

While most of the porous capping layer 54 is vaporized during annealingof the intermediate product to form a next-stage product, residualmaterial from the layer 54 which is not vaporized, as shown in FIG. 1D,can be removed by a dry cleaning or plasma cleaning process, or a wetetching process. In a suitable dry cleaning or plasma cleaning process,a process gas comprising fluorine, such as CF₄ can be introduced intothe process zone 46, and a plasma generated from the process gas is usedto clean off residual silicon- and oxygen-containing material from thesurface of the substrate 40. The resultant substrate 40 comprises ionimplanted regions 44 a,b which have uniformly distributed ionconcentrations, reduced lattice defects, and a clean surface 58 as shownin FIG. 1E.

An exemplary embodiment of an integrated circuit comprising PMOS andNMOS transistors that can be fabricated using the present process isillustrated in FIG. 3. In this structure, a substrate 40 comprising asilicon wafer, has an active semiconductor layer 100 a,b which can bethe bulk semiconducting silicon material (as shown), or a silicon island(not shown) formed on an insulating layer over the substrate 40. A PMOStransistor 102 is formed in a lightly n-doped region 100 a of the activelayer 100, and an NMOS transistor 202 is formed in a lightly p-dopedregion 100 b of the active layer 100. The p- and n-doped regions 100 a,100 b, are insulated from one another by a shallow isolation trench 106etched into the active layer and filled with an insulating material suchas silicon dioxide. The PMOS transistor 102 also includes heavilyp-doped source and drain regions 108 a, 108 b in the active layer andheavily p-doped source and drain extensions 110 a, 110 b separated by ann-doped channel 112.

The ion implanted regions 44 a,b can be, for example, any one of thelightly n-doped region 100 a, lightly p-doped region 100 b, heavilyp-doped source and drain regions 108 a, 108 b, and heavily p-dopedsource and drain extensions 110 a, 110 b, which are separated by ann-doped channel 112. In this version, immediately after deposition ofany of the ion implanted regions 44 a,b, a porous capping layer (notshown) is used to cover the ion implanted regions 44 a,b to preventvolatilization of the ions during a subsequent annealing process thatcan be performed on the substrate 40. Thereafter, the substrate 40 withthe ion implantation regions 44 a,b is annealed. In the annealingprocess, substantially all of the porous capping layer 54 vaporizes.Thereafter, others layers are deposited, etched and otherwise processedonto the substrate 40.

In the PMOS transistor 102, a polycrystalline silicon gate electrode 114overlies the channel 112 and is separated from it by a thin gate silicondioxide layer 116. A gate contact 118 comprising for example, titaniumsilicide or cobalt silicide, overlies the gate electrode 114. A sourcecontact region 120 also comprising, for example, titanium silicide orcobalt silicide, is formed in the source region 108 a. A silicon nitrideinsulation layer 122 overlies the source and drain region 108 a, 108 band surrounds the gate electrode structure 114, 116, 118. Silicondioxide islands 124 lie within the insulation layer 122. A thin siliconnitride etch stop layer 126 overlies the PMOS transistor 102. The bottominsulation layer 130 of an overlying multiple interconnect layer 132overlies the etch stop layer 126. After the insulation layer 130 isformed, a chemical mechanical polishing process can be used to flattenits top surface 130 a. A metallic source contact 134, such as forexample, tin, extends vertically through the insulation layer 130 andthrough the etch stop layer 126 to the titanium silicide source contactregion 120. The insulation layer may be silicon dioxide (SiO₂), orsilicon dioxide-containing combinations such as phosphorus silicateglass (PSG), boron silicate glass (BSG) or carbon-doped silicate glass(CSG). Such combinations can be formed in a plasma-enhanced depositionprocess using a process gas containing an oxygen-containing gas, asilicon precursor (e.g., silane), phosphorus precursor gas (PH₃), boronprecursor gas (B₂H₆) or carbon-containing gas.

The NMOS transistor 202 includes heavily n-doped source and drainregions 208 b, 208 a in the active layer and heavily n-doped source anddrain extensions 210 b, 210 a separated by a p-doped channel 212. Apolycrystalline silicon gate electrode 214 overlies the channel 212 andis separated from it by a thin gate silicon dioxide layer 216. A gatecontact 218 comprising, for example, titanium silicide overlies the gateelectrode 214. A titanium silicide source contact region 220 is formedin the source region 208 b. A silicon nitride insulation layer 222overlies the source and drain region 208 b, 208 a and surrounds the gateelectrode structure 214, 216, 218. Silicon dioxide islands 224 liewithin the insulation layer 222. A thin silicon nitride etch stop layer226 overlies the NMOS transistor 202. The bottom insulation layer 130 ofthe overlying multiple interconnect layer 132 overlies the etch stoplayer 226. A metallic (e.g., TiN) drain contact 234 extends verticallythrough the insulation layer 130 and through the etch stop layer 226 tothe titanium silicide source contact region 220.

An exemplary embodiment of a substrate processing apparatus 300 suitablefor implanting ions to form the ion implanted regions 44 a,b in asubstrate 40, and also capable of depositing the porous capping layer 54over the implanted regions 44 a,b in the same process zone 46, is shownin FIG. 4. The substrate processing apparatus 300 can be, for example, atorroidal source plasma immersion ion implantation apparatus, such asthe P3I™, commercially available from Applied Materials, Santa Clara,Calif. A suitable apparatus is described in, for example, U.S. PatentApplication Publication No. 2005/0191828, to Al-Bayati et al., filed onDec. 1, 2004, which is incorporated by reference herein and in itsentirety.

Generally, the apparatus 300 comprises a process chamber 310 enclosed bya cylindrical side wall 312 and a disk-shaped ceiling 314. A substratesupport 316 in the chamber 310 comprises a substrate receiving surface318 for supporting a substrate 40 for processing of the substrate in aprocess zone 46. The substrate support 316 can be an electrostatic chuck317 which includes an electrode 319 embedded in, or covered by, adielectric plate 321. The electrode 319 is powered by a chuck DC voltagesource generator 323.

A process gas comprising ion implantation gases that contain the speciesto be ion implanted into the substrate 40 is introduced into the processzone 46 through the gas distributor 320. The gas distributor 320 on theceiling 314 of the chamber 310 receives the process gas via a gasmanifold 324 connected to a gas distribution panel 325. The gas manifold324 is fed by the individual gas supplies 326 a-j which are individuallycontrolled by a set of mass flow controllers 327 a-j that set the flowof a gas from each gas supply 326 a-j to control the composition of theprocess gas. For example, the individual gas supplies 326 a-j caninclude supplies of arsenic-containing gas, phosphorus-containing gas,boron-containing gas, carbon-containing gas, hydrogen, oxygen, nitrogen,silane, germanium-hydride gas, krypton, xenon, argon, or other gases.The gas supplies 326 a-j can contain different dopant-containing gasesincluding fluorides of boron, hydrides of boron, fluorides ofphosphorous and hydrides of phosphorous. Other gases include gases usedin co-implantation (hydrogen and helium), material enhancement(nitrogen), surface passivation or co-implantation (fluorides of siliconor germanium or carbon), and photoresist removal and/or chamber cleaning(oxygen gas). A vacuum pump 328 is coupled to a pumping annulus 330defined between the substrate support 316 and the sidewall 312.

The process gas is energized in the process zone 46 above the substrate40. A gas energizer 333 suitable for energizing the process gas in theprocess zone 46 includes a pair of external reentrant conduits 334, 336,which establish reentrant torroidal paths for plasma currents that passthrough, and intersect in, the process zone 46. Each of the conduits334, 336 has a pair of ends 338 coupled to opposite sides of the chamber310. Each conduit 334, 336 is a hollow conductive tube and has a D.C.insulation ring 340 which prevents the formation of a closed loopconductive path between the two ends of the conduit. An annular portionof each conduit 334, 336, is surrounded by an annular magnetic core 342.An excitation coil 344 surrounds the core 342 and is coupled to an RFpower source 346 through an impedance match device 348. The two RF powersources 346 coupled to respective cores 344 may be of two slightlydifferent frequencies. For example, the gas energizer 333 can forminductively coupled plasma from the process gas by applying an RFcurrent having a frequency of 400 kHz and 15 MHz. The RF power coupledfrom the RF power generators 346 produces plasma ion currents in closedtorroidal paths extending through each respective conduit 334, 336 andthrough the process zone 46. These ion currents oscillate at thefrequency of the respective RF power source.

During the ion implantation process, the gas energizer 333 applies asource power from the RF generators 346 to the reentrant conduits 334,336 to create torroidal plasma currents in the conduits and in theprocess zone 46. Bias power is applied to the substrate support 316 by abias power generator 349 through an impedance match circuit 350. The ionimplantation depth is determined by the substrate bias voltage appliedby the RF bias power generator 349. The ion implantation rate or flux,which is the number of ions implanted per square cm per second, isdetermined by the plasma density, which is controlled by the level of RFpower applied by the RF generators 346. The cumulative implant dose(ions/square cm) in the substrate 40 is determined by both the flux andthe total time over which the flux is maintained.

When the porous capping layer 54 is deposited on the substrate 40, thesource power generators 346 can be used without using the bias powergenerator 349 to generate a plasma without accelerating ions towards thesubstrate 40. In this process, the process gas is dissociated to formions, neutrals and other species that react with one another or thesubstrate surface to deposit the porous capping 54 layer on thesubstrate 40.

In either the ion implantation or capping layer deposition processes,alternative sources of energy can be used to form a plasma, energizeions, and react the process gas. For example, instead of inductivecoupling, a plasma can also be generated using any conventional or highdensity plasma generating source, including for example, capacitiveplasma sources, electron cyclotron resonance, or transformer coupledplasma. Thus, the scope of the present claims should not be limited tothe exemplary apparatus described herein.

The present invention has been described with reference to certainpreferred versions thereof; however, other versions are possible. Forexample, alternative ion implanting processes can also be used. Also,different materials can be used for the capping layer 54 as would beapparent to those of ordinary skill in the art. Therefore, the spiritand scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

1. An ion implantation method comprising: (a) implanting ions into aregion of a substrate to form an ion implanted region; and (b)depositing a porous capping layer on the ion implanted region, theporous capping layer comprising dispersed gas pockets.
 2. A methodaccording to claim 1 wherein (b) comprises depositing a porous cappinglayer comprising dispersed gas pockets that are microscopic gas pockets.3. A method according to claim 1 wherein (b) comprises depositing aporous capping layer having at least one of the following properties:(i) a porosity of at least 20%; or (ii) a pore volume of at least 20%.4. A method according to claim 1 wherein (b) comprises depositing aporous capping layer comprising silicon and oxygen.
 5. A methodaccording to claim 1 wherein (b) comprises depositing a porous cappinglayer comprising silicon dioxide.
 6. A method according to claim 5comprising depositing the silicon dioxide by energizing a process gascomprising silane and oxygen.
 7. A method according to claim 1comprising during (a) or (b) maintaining the substrate at a temperatureof between about 25° C. and about 400° C.
 8. A method according to claim1 further comprising annealing the substrate to volatilize at least aportion of the porous capping layer.
 9. A method according to claim 1comprising annealing the substrate to volatilize at least 90% of theporous capping layer while retaining at least 60% of the implanted ionsin the ion implanted region.
 10. A method according to claim 1 wherein(a) comprises implanting ions comprising arsenic, boron or phosphorous,in a dosage from 1×10¹⁴ atoms/cm³ to 1×10¹⁷ atoms/cm³.
 11. A methodaccording to claim 1 wherein (a) comprises implanting arsenic ions byenergizing a process gas comprising an arsenic-containing gas.
 12. Anion implantation method comprising: (a) implanting ions into a region ofa substrate to form an ion implanted region; (b) depositing a porouscapping layer on the ion implanted region, the porous capping layercomprising dispersed microscopic gas pockets; and (c) annealing thesubstrate to volatilize at least 80% of the porous capping layeroverlying the ion implanted region during the annealing process.
 13. Amethod according to claim 12 wherein (b) comprises depositing a porouscapping layer having at least one of the following properties: (i) aporosity of at least 20%; or (ii) a pore volume of at least 20%.
 14. Amethod according to claim 12 wherein (b) comprises depositing a porouscapping layer comprising silicon and oxygen.
 15. A method according toclaim 12 wherein (b) comprises depositing a porous capping layercomprising silicon dioxide.
 16. An ion implantation method comprising:(a) implanting arsenic ions into a region of a substrate to form an ionimplanted region; (b) depositing on the ion implanted region, a porouscapping layer comprising silicon-containing material having dispersedmicroscopic gas pockets; and (c) annealing the substrate to volatilizeat least 80% of the porous capping layer overlying the ion implantedregion during the annealing process.
 17. A method according to claim 16wherein (b) comprises depositing a porous capping layer comprisingsilicon dioxide.
 18. A method according to claim 16 wherein (a)comprises implanting the arsenic ions using a process gas comprisingarsenic fluoride or arsenic hydride.
 19. A method according to claim 16wherein (a) comprises maintaining the substrate at a temperature ofbetween about 25° C. and about 400° C.
 20. A method according to claim16 wherein (c) comprises annealing the substrate to a temperature offrom about 800° C. to about 1300° C.